Automatic trunking system.



5.0. FALE S. AUTOMATIC TRUNKING SYSTEM.

APPLICATION FILED MAY 17, I909. 9,34 Patented Dec. 4,1917".

3. SHEETS-SHEET I JWZWOR- I/V/T/VESSES E. D. FALES. AUTOMATIC TRUNKINGSYSTEM.

APPLICATION FILED MAY I]. 1909. 1,248,834. Patented Dec. 4, 191 7.

3' SHEETS-SHEET 2- n1 l l l l l l H ZZZ/Z5555 2- E. D. FALES.

AUTOMATIC TRUNKING SYSTEM.

APPLICATION FILED MAYH. I909.

1,248,834. Patented Dec. 4, 1917.

3 SHEETSSHEET 3.

UNITED STATES PATENT OFFICE.

EDWARD D. FALES, OF LA GRANGE, ILLINOIS, ASSIGNOR TO AUTOMATIC ELECTRICCOMPANY, OF CHICAGO, ILLINOIS, .A CORPORATION OF ILLINOIS.

AUTOMATIC TRUNKING SYSTEM.

Specification of Letters Patent.

Patented Dec. 4, 1917.

. Application filed May 17, 1909. Serial No. 496,591.

tems, of which the following is a specifica tion.

My invention relates to telephone exchange systems of that particularcharacter in which the apparatus for extending a trunking connection inthe direction of the called subscriber is controlledover the two sidesof the line circuit in series. Heretofore in systems of this kind thearrangement has been such that the closure of the line circuit at thecalling subscribers substation, by the removal of the receiver from theswitch hook, caused an automatic switch at the exchange or centralstation to seize an idle trunk line. Obviously, therefore, it waspossible for a subscriber to take down his receiver, thereby causingconnection to be made with a trunk line, and to then defer making thecall for more or less time, there by excluding the said trunk line fromuse by other subscribers. When the calling subscriber operates hiscalling mechanism the connection is then completed from the said trunkline to the called line. As stated, and

during the interim between the removal of the receiver and the operationof the calling mechanism, the said trunk line could not be used by othersubscribers, notwithstanding that the said calling subscriber was notactu ally using it for talking purposes. This tended to reduce theefiiciency of the service, as while a subscriber who had taken off hisreceiver was waiting to make the call, thetrunk line which he wasthereby monopolizing for no useful purpose was not available for use byother subscribers.

The object of my invention is, therefore,

the provision of an improved construction.

and arrangement whereby, in a system of this particular character, theremoval of the receiver at the calling substation will not cause thesubscribers line switch or other similar mechanism to seize an idletrunk line, and whereby suchseizure of the trunk line does not occuruntil the calling subsoriber actually begins operatingthe callinmechanism, as by rotating the ordinary an well-known rotary dial, thusmaterially increasing the trunking efficiency of the ex change, andmaking it possible to give eifi- 'cient service with a less number oftrunks than was heretofore possible in a so-called two-wire systemthatis to say, a system in which the automatic selecting and connectingmechanism at the exchange or central station is controlled over the twosides of the subscribers line in series, there being no operatinggrounds at the substations.

To this, and other useful ends my invention consists in mattershereinafter set forth and claimed.

In the accompanying drawings Figures 1 and 2 are a diagrammaticrepresentation of a circuit connection established between a callingsubstation in Fig. 1 and a called substation in Fig. 2, in a systemembodying the principles of my invention.

.Figs. 3 and 4 are a side and front elevation, respectively, of myimproved subscribers individual or line switch.

Fig. 5 is a partial plan view of the switch shown in Figs. 3 and 4,showing features of my invention. I v To the substation A (Fig. 1) thereis allotted the individual line switch C. This line switch C, togetherwith a number of other similar switches, is controlled by a commonmechanism D, usually called a master switch. Accessible to the lineswitch C is the numerical switch E, commonly called a first selector.This first selector E is one of a group of selectors common to a groupof line switches C. At F is shown a socalled second selector, which isone of a group of selectors common and accessible to a number of firstselectors E. Accessible to a group of second selectors F are a number ofconnectors H, by which connection may be completed to a group ofsubstations of which A is a member. To the substation A there isallotted at the exchange a line switch C similar to the line switch C ofsubstation A. The line switch C is controlled by a master switch similarto D (Fig. 1). The line switches C and C may be controlled by the samemaster switches, or by different ones. depending upon whether or not thetwo substations A and A belong to the same group. At B is shown abattery, with one terminal grounded, for supplying current for operatingthe central station apparatus, and providing talking current for theconnected substations.

Although the line switch C is shown with only one set of trunkterminals, it is provided with a'bank containing the terminals of anumber of trunks, each leading to a selector E. Each trunk has aterminal in the bank of each line switch of the group. Like-v tors F aresimilar to those of the first selectors E, the trunks therefrom leadingto connector H.

In order to secure connection with the subscriber A (Fig. 2) thesubscriber at A removes his receiver and o erates his call ing deviceonce for each digit of the number of the substation A. The firstoperation of the dial operates the line switch C, causing it to extendthe connection from the line of substation A to a pre-selected trunkleadin to an idle selector F. The master switch then operates theremaining idle line switches to place them in such position that thenext one that operates will not seize the trunk already occupied by C,but will make connection with an idle selector. The

operation of the dial.for the next digit ad- In the same manner theoperation of the calling device for the next digit carries the secondselector to establish connection with an idle connector H. The operationof the calling device for the last two digits operates the connector Hto complete the connection with the desired line.

The substation A (Fig. 1) may be of any suitable or approved type. Ashere shown, the substation comprises a receiver 2, switch hook 3,impulse wheel 4, transmitter 5, induction coil 6, impulse springs 7 and8, ringer 9 and condenser 10. When the receiver is on the hook it holdsthe hook down and thereby maintains the springs 13 and 14 in contact,thus bridging the ringer 9 and condenser 10 in series across the lineconductors 16 and 17. When the receiver isremoved from the hook,however, the switch hook is forced upward by a spring (not shown) whichallows the spring 13 to leave sprin 14 and engage spring 15. By thisaction t e circuit 0 the ringer 9 is opened and a bridge, consisting ofthe impulse springs into the bank, forcing t shown). When the dial ispulled down the impulse wheel is advanced a certain-number of teeth,corresponding to the digit called, but with no effect on the impulsesprings 7 and 8. When the impulse wheel is released, however, it isreturned to normal positlon by a spring, and each tooth. that passes theimpulse springs forces them apart, thus sending a series of impulses tothe exchange switching apparatus.

The line switch O,-the mechanism of which is shown in Figs; 3, 4 and 5,consists essentially of a plunger 18 carried on a plunger arm 19, and amagnet 20. The plunger arm 19 is held in its, normal position by thespring 21, but when the said arm is attracted by the magnet 20 theplunger 18 is thrust esprings 22, 23, 24, 25, 26, 27, 28 and 29 'intocontact in pairs, as indicated in Fig. 1. The magnet 20 is composed ofthree windings, a pull-inwinding 30, a bridge-cut-ofi winding 31 and aline winding 32. The pullin winding 30 is for the purpose of attractingthe plunger arm 19 to thrust the plunger 18 into the bank.

The circuit of the pull-in winding 30 is controlled by the wiper 33, thesaid wiper being in turn controlled by the. calling subscriber throughthe medium of the line winding 32.

The magnetic circuit of the line windin 32 is entirely independent ofthat of the wmdings 30 and 31, so that when the said wind? ing 32energizes it affects only the armature 34. The wiper 33 is held innormal position, against the tension of the spring 35 (Fig. 5), by thefinger 36 resting against the rear tooth of the upper escapement spring37. The lower escapement spring is so set that the rear edge of thetooth 38 is a short distance in. advance'of the upper .tooth. If, now,the armature 34 is attracted thelower point of the tooth on the upperescapement spring rises above the arm 36, and the said arm moves outinto engagement with the tooth 38. Now when the armature restores, thelower tooth comes down on top of the beveled edge of the finger 36, andthecsaid finger escapes and flies out against the stop tact with thecontact 39, thereby closing anenergizing circuit through the pull-inwlnding 30. With this escapement arrangement .it is seen that thecircuit through the pullin winding is not closed until the line winding32 has been energized and denergizod again. After the plunger arm hasbeen once pulled down it may be held in its operated.

position by the cut-off winding 31. If the cut-off winding is energizedwhile the plunger arm is in its normal position, only the cut-offarmature 40 will be operated. To

the under side of the plunger arm 19 is attached an arm 41 whichprojects through an opening in the lower part of the switch lever 42.When the plunger arm is drawn down it forces. the arm 41 downward also,

and the beveled end striking the end of the lever 42 'forces it outward.The other end ofithelever .42 carries a vertical stop 38 which-movesback and forces the finger 36 and wiper 33 back into normal position,

when the other end of the lever 42 is forced outwardby the arm 41. Oneend of the plunger .18 is broadened out "into a fan like projection witha notch in its center. This notchnormally engages .the plunger shaft 43,so that the plungers may be moved from one trunk to another by therotation of said shaft. The movement of the plunger shaft is controlledby the master switch D. The master switch D consists essentially ofa-motor magnet 44 which operates .the

ratchet-wheel 45, a bank of contacts a and the circuit COIltIOlliIlgrelays 46, 47 and 48'.

The master, switch bank a is composed of.

a common segment 50 and a number of individual segments 1), and a wiper49 is pro vided for keeping some one of the individual segments alwaysin electrical connection with the common segment 50. By means of asuitable mechanical connection the rotary motion of the ratchet wheel 45is transmitted to the plunger shaft 43 to give the said shaft areciprocating motion. To the plunger shaft is rigidly secured a cam. 51,

selector E is provided with the usual vertihaving on its surface anumber of circular openings which are engaged by a pin 87 on thearmature 52 when the relay 47 is deenergized, thereby locking theplungers in front of a trunk. 1

The selector switch E is of the eneral type shown in United StatesLetters atent No. 815,321, issued March 13, 1906, to Keith, Erickson andErickson, but as here shown is adapted to operate in conjunction with atwo-wire systemi. 6., a systemin which there is no ground at thesubstation; The

cal magnet 53, rotary magnet 54 and release magnet 55. The usual sideswitch is composed of the wipers 56, 57, 58 and 59, and

is controlled by private magnet 60. The usual line relays .are here'combined in the double wound relay 61. Relay 62 controls .the releasecircuit and relay63 controls the private magnet circuit.

The second selector F is with the first selector E.

The connector H is of the type disclosed in United States Letters Patent#815,176, granted March 13, 1906, to Keith, Erickson and Erickson, but,like the second selectors E and F, is adapted to operate inconjuncalmost identical tion with a two-wire system. Like the'selectors,the connector has a double wound line relay 63, vertical magnet 64,rotary magnet 65, release magnet 66, prlvate magnet 69,

private magnet relay 68, release relay 67 and a sideswitch. In additionthe connector is provided with a back-bridge relay 70,

.the apparatus involved in a connection between two subscribers, themethod of establishing such a connection willbe given in detail. With myinvention one complete impulse is required to operate the line switch'before any impulses can be delivered to the numerical switchingapparatus.

This preliminary impulse may be produced in a number of diflerent ways,but for the purpose of'description I have assumed that an I extra digit(1) is prefixed to the regular exchange number of the line. In orderthat the subscriber at substation A may call substatlon A, the number ofwhich has been assumed to be 12220, he removes his receiver from thehook and then operates his dial once for each of the five digits of thedesired number.

As soon as the receiver 2 is removed from the switch hook the springs 13and 15 engage, closing a bridge across the line conductors, as hasalready been explained. The closure of this bridge also closes a circuitthrough the line winding 32 of the, line switch C. This circuit extendsfrom ground G through springs 72 and 73, line conductor 16, thencethrough thesprings 13 and 15, impulse springs and 8, primary winding ofinduction coil 6, transmitter 5, line conductor 17 springs 74 and 75,and through line relay 32 tothe battery lead 76, thence through thebattery B to ground G. The energlzation of winding 32 has no eflectother than to draw up the armature 34. The subscriber now operates thedial for the digit 1, whereby the impulse springs 7 and 8 aremomentarily forced apart. When the springs 7 and 8 separate, theenergizing circuit of the winding 32 is broken, and the armature 34falls back, which allows the circuit of the line winding 32 byseparating springs 73 and 74 from springs 72 and 75. When the plungerenters the bank the bank springs 22, 24, 26 and 28 are forced intoengagement with the springs 23, 25, 27 and 29, respectively. Theengagement of springs 22 and 28 with springs 23 and 29 closes anenergizing circuit from ground G through the lower winding of relay 61of the selector E, thence through the substation A and back through theupper winding of relay 61 to the battery B. The relay 61 energizes uponthe closure of this circuit and closes an energizing circuit through therelease relay 62. This circuit extends from ground Gr through springs 78and 79, and through relay 62 to battery B. The relay 62 thereuponenergizes and shifts spring 80 from 81 into contact with 82, and alsocloses springs 83 and 84. The closure of springs 83 and 84 furnishes anenergizing circuit from ground G through the bank springs and 24,andthrough the cut-off winding 31. This energizing of the winding 31 isfor the purpose of holding the plunger arm 20 and cut-off armature 40 intheir operated positions. The energization of the re lease relay 62 ofthe selector E also grounds the private normal conductor 172 for pro-\iding a guarding potential at the connector private bank contacts ofthe calling line to protect the said calling line from being calledwhile it is busy. At the time the plunger arm 20 is pulled down thewiper 33 is restored b the arm 41, and opens the circuit of pull-1nwinding 30. To provide for the possibility of the pull-in windingcircuit being opened before the relay 62 has time to close the circuitof the cut-01f winding 31, the-slow relay 46 is included in theenergizing circuit of. the winding 30. When the relay 46 energizes itcloses the springs 85 into contact, thereby furnishing an ener gizingcircuit through the winding 31 from ground G The relay 46 is slow todeenergize and maintains the connection between the winding 31 and theground G for a short time after the circuit of the said relay andwinding 30 is opened, thus giving the relays 61 and. 62 of the selectorE time to energize and supply a new holding ground before ground G iscut off.

When the bank springs 26 and 27 are closed a connection is extended fromground G to the master switch bank contact 86. When the idle plungersare opposite the trunk of selector E the wiper 49 is resting on thewiper 86, so that when ground comes on the contact 86 it energizes therelay 48 over the said wiper 49, common segment 50, through said relay48 to battery B. The relay 48, upon energizing, closes an energizingcircuit from ground Gr through the locking relay 47 to battery B. Therelay 47, upon energizing, attracts its armature, withdrawin the pin 87from the opening in the cam 51 in which it is resting, and places saidarmature in contactwith contact point 88. The engagement of the armature52 with contact point 88 establishes an energizing circuit for the motormagnet 44. The

energizing circuit ofthe motor magnet in-.

cludes the interrupter springs 89, so that the magnet 44 operates like abuzzer to give the wheel 45 a continuous rotary motion, moving the idleplungers and the wiper 49 away from the trunk just seized. As soon aswiper 49 leaves the contact 86, the relay 48 and, consequently, therelay 47 denergize. The energizing circuit of the motor magnet, however,is not broken immediately upon the denergization of relay 47 be causethe previously mentioned opening in the cam 51 has passed out ofregister with the pin 87, so that the armature 52 cannot fall back.After the denergization of relay 47, the master switch continues tooperate until the next opening in the cam 51 passes under the pin 87,when the armature 52 falls back, opening the circuit of the motor magnet44 and locking the plunger shaft with its engaged plungers opposite anidle trunk. If the next trunk after the one seized had been idle, the,wiper 49 would have found the corresponding bank contact grounded, therelay 48 would not have deenergized and the plungers would have beencarried onto the next trunk which was idle.

When the armature 52 of the relay 47 pulls up, it leaves the contact 77,and thereby disconnects the battery from the pull-in winding of all theline switches which it controls; therefore, no line switch can beoperated while its master switch is moving. This prevents a line switchfrom operating before its plungerhas reached an idle trunk.

The calling subscriber is now ready to operate his calling device forthe second digit (2). As the impluse wheel 4 returns to normal for thisdigit, the impulse springs 7 and 8 are forced apart twice,'thus allowingthe relay 61 of the selector E to deenergize twice. Each time the relay61 deenergizes, the spring 78 leaves spring 79 and engages spring 89.The relay 62 is slow to deenergize and the time during which the springs78 and 79 are separated is so short that the relay 62 does not return toits normal position while the impulses are being sent in. Each time thespring 78 engages the spring 89 an energizing circuit is closed fromground Gr through springs 78 and 89, through springs 80 and 82, throughrelay 63, vertical magnet 53, and side switch wiper 58 (in firstposition) to battery B. The vertical magnet responds to the two impulses.and operates to raise the switch shaft and wipers 91, 92 and 93 twosteps. The relay 63 energizes upon the first impulse but, being slow todenergize d s not have time to return to its normal p ition' until afterall the impulses for the second digit are completed. The energization ofthe relay 63. completes an energizing circuit from ground G through thecircuit of the private magnet.

private magnet '60. After the last impulse the relay 63 deenergizes,allowing the springs 94 and 95 to separate and open the When the privatemagnet deenergizes, it allows the side switch topass from first tosecond position, whereby a circuit is closed through the rotary magnet54. This circuit extends when the rotary magnet energizes, its armaturepresses down the private armature, and

when the rotary armature falls back, the private armature alsorestorestifthe first trunk' is idle) and allows theside switch to passinto third position. If the first trunk is busy, however, the privatewiper 93 finds a grounded contact, said ground being supplied by someother occupying switch.

When the private wiper 93 thus strikes a grounded contact, it forms alocking circuit for the private magnet 60, through the side switch wiper.59 in second, position. :The private magnet thus locks the side switchin second position, and the rotary 'magnet continues to rotate the shaftstep by step until the wiper 93 finds a non-grounded contact, when theprivate magnet is allowed to deenergize, and the side switch passes tothird position, as before explained. As soon as the side switch passesto third position, the circuit of the rotary magnet is opened by thewiper 58, the line relay 61 is cut ofl of the line by the wipers 56andt57, and the connection is extended through to the second selector F.As soon as the connection is extended to the second selector F, the linerelay 97 energizes and closes an energizing circuit for the relay 98.This circuit extends from ground Gr through springs 100 and 101, andthrough the relay 98 to battery. The relay 98, upon energizing, extendsa connection from ground G? through springs 102 and 103, private wiper93, side switch wiper 59 in third position, and through the'relay 62 tobattery. This circuit maintains the relay 62 energized after the cuttingoff of the ground G1 upon the deenergization of relay 61-, when it iscutfrom the line.

When the calling device is operated for the third digit (2), the linerelay 97 of the second selector F responds, and the second selectoroperates in the same manner as explained for the first selector E, to,extend the connection to an idle connector H, which has access tothegroup of lines of which A is a member. Thus, when the two impulses forthe third digit are sent in, the vertical magnet 104 is energized twiceto raise the shaft wipers 105, 106 and 107 two steps. first impulse andcloses the energizing circuit of the private magnet 109. After the lastimpulse the private magnet deenergizes, and allows the side switch topass to second position, thus closing'the circuit of the rotary magnet109. The rotary magnet then operates to rotate the shaft wipers onto theterminals of an idle trunk leading toa connector H, after which the sideswitch passes to third position, opening the circuit'of the rotarymagnet 109 at the wiper 110. Also,

The relay 108 is energized by the when the side switch wipers 111 and112 pass from second to third position, the line relay 97 is cut offfrom the line, and the connection from the substation A- is extended tothe connector H over the line.

wipers 105 and 106, and conductors 170 and 171.

When the connection is thus extended to I the connector, the doublewound line relay 63 energizes and closes an energizing cir- I the relay97 deener 'zes. "This circuit extends from ground through side switchwiper 113, relay springs 114 and 115, conductor 116, private wiper 107of selector F, side switch wiper 117 in third position, and throughrelay 98 to the battery lead 7 6. The energizing circuit of the linerelay 63 of the connector H extends from ground G11 through the lowerwinding of the said relay to conductor 171, thence over the heavyconductors in Fig. 1,-through the switches F, E and 0 through thesubstation A, thence back through switches C, E, and F, and through theupper winding of relay 63 to the battery lead 76. The circuit which isvI closed through the relay 67 by the relay 63 extends from ground G12through springs 118 and 119, and relay 67 to the battery lead 76, thencethrough the battery B to ground G. When the relay 67 energizes, it com-.

pletes a connection via springs 122. and 121,

between the vertical magnet 64 and the spring 120 of the relay 63,whereby impulses may be transmitted to the vertical magnet 64.

The switches are now in'position to receive impulses for the fourthdigit (2).

The two impulses for this digit cause the reremains in its operatedposition until after the last impulse. By the closure of springs 143 and125 the relay 68 closes an energizing circuit from ground G through theprivate magnet 69 to battery. The private magnet 69, upon energizing,places the springs 126 and 127 in contact, without any effect at thistime, however. After the last impulse, the private magnet relay 68deenergizes and opens the circuit of the private magnet 69. When theprivate magnet denergizes, the side switch passes from first to secondposition. The movement of the side switch wiper 128 from first to secondposition disconnects battery from the vertical magnet 64 and connectsthe rotary magnet 65 with the battery B through the private magnet relay68. When the calling device is operated for the last digit (0), therelay 63 responds ten times, and sends ten impulses from ground G12through springs 118, 120, 122, 121, 129 and 130, rotary magnet 65, sideswitch wiper 128, and relay 68 to battery. These ten impulses to therotary magnet cause the shaft wipers 131, 132 and 154 to be rotated ontothe tenth contacts of the second bank level, which are the contacts ofthe desired line #12220. The private magnet 69 is energized during thetime the impulses are coming in, in the same manner as when the verticalmagnetwas operated. When the private magnet deenergizes, upon thecessation of theimpulses, the side switch passes to third position andcompletes the connection between the two substations. If the called lineis busy, however, when called, the private magnet cannot deenergize, butlooks the side switch in second position, thus preventing the completionof the connection. The manner in which the side switch is thus locked isas follows: Whenever a line is busy, either having made a call or havingbeen called, a guarding ground potential is placed upon all of theconnector bankcontacts of that line. Thus if the called line is busy,the private wiper 154 finds the contact which it encounters grounded.This ground is extended via springs 133 and 134 of relay 71, lowerwinding of relay 70, ringer relay springs 135 and 136, side switch wiper137 in second position to the spring 139 of the private magnet relay 68.The private magnet relay springs are so adjusted that, as the relaydeenergizes, the spring 125 engages spring 139 before it leaves thespring 143. Thus, when the relay 68 deenergizes after the last impulseto the rotary magnet, a new circuit is closed from spring 139 throughthe private magnet 69 to battery, thus holding the said magnet in itsoperated position, and the side switch can not ass to third-position.Since the lower windlng of the back bridge relay is included in the newholding circuit of the private magnet, the said relay 7 0 energizes,separating springs 139 and 140, and closing springs 141 and 142. Whenthe relay 68 deenergizes, the springs 143 and 144 again engage, wherebya circuit is closed from ground (al through springs 143, 144, 126 and127, busy locking relay 71, and

springs 142 and 141 to the battery B. The

relay 71 energizes upon the closure of this circuit and, by theengagement of springs 145 and 134, furnishes a new locking ground forthe private magnet 69, independently of the ground at the private bankcontact. Also, when the relay 71 energizes while the side switch is yetin second position, the calling subscriber is given a busy signal over acircuit as follows: from the battery lead 76 through the secondarywinding of the busy signaling machine J, through springs 146 and 147,side switch wiper 148, ringer relay springs 149 and 150, thence throughthe condenser 151 and over the heavy conductors, through the switches F,E and C, through the receiver of the called substation, thence backthrough the switches C, E and F, and a through the winding of coil 63 toground, and thence through the battery B to the startin point. When thecalling subscriber hears t is busy signal he hangs up his receiver, andthe switching mechanism is restored in a maner which will be explainedlater. If the called line is not busy, the private wiper 154. does notfind its contact grounded and, consequently, the circuit of the privatemagnet 68 is opened when the relay 68 falls back, after the last impulseto the rotary magnet, and the side switch passes to third position. Whenthe side switch wiper 152 reaches its third position contact point, aguarding ground is placed upon the private wiper 154 and, consequently,upon all the private bank contacts of the called line, and an energizingcircuit is closed through the bridge-cut-ofi' winding 153 of the lineswitch C. This energizing circuit extends from ground Gr through sideswitch wiper 152, relay springs 133 and 134, private wiper 154, andthrough the Winding 153 to battery. The winding 153, upon energizing, isnot strong enough to operate the plunger arm 155 from its normalposition, but ulls down the cut-off armature 156, there y cutting offthe line winding 157 from the called line. When the side switch wiper128 reaches third position, a circuit is closed from ground G throughthe interrupter 158, relay springs 139 and 140, ringer relay 169, sideswitch wiper 128, and private magnet relay 68 to the battery lead 76.The relays 169 and 68 are intermittently energized over this circuit bythe interrupter 158. The relay 68 causes the function. Each time thatthe ringer relay BEST AVAlLABLE springs 159 and 149, side switch wiper14:8,

line wiper' 131, line conductor 161. ringer 163,, condenser 164,conductor 162, line wiper 132, side switch wiper 137, relay springs 136and 160 to the other terminal of the generator I. In response to thesignal the subscriber at-substation A removes the receiver from theswitch hook, whereby the circuit 6 of the ringer 163 is opened, and thetransmitter 165 and primary winding of the induction coil 166 arebridged across the line conductors 161 and 162. The first time theringer relay denergizes, after the talking set is bridged across thetalking conductors of the called substation, that substation is providedwith talking battery current over the following circuit: from ground G15through the side switch wiper 152, lower winding of the back-bridgerelay 70, ringer relay springs 135 and 136, side switch wiper 137,thence through the substation and back through the side switch wiper148, relay springs 119 and 150, and through the upper winding of relay 70 to battery. The relay 70, being included in the circuit just traced,energizes and operates the springs 139 and 1 10, thereby opening thecircuit of the ringer relay 169, so that the said relay cani not againenergize after the called subscriber answers.

After a connection hasbeen completed, or

after the connector has been locked on a busy called line, the releaseof all the switches is initiated by the return of the receiver to thehook at the calling substation. \Vhen the receiver at substation A isthu restored the circuit of the relay 63 of the connector H is opened bythe separation of the substation springs 13 and 15, due to the downwardmovement of the switch hook. When the circuit of the relay 63 is openedthe said relay dencrgizes and allows the springs 118 and 119 toseparate, whereby ground is disconnected from the. release relays 67and98 of the connector H and selector F, respectively. This is strictlytrue only when releasing after a complete connection. \Vhen releasingfrom a busy line the side switch wiper 113 of the connector is still insecond position, and, consequently, the ground is not out 01f from therelease relay of the second selector F until the relay 67 of theconnector deenergizes and permits the springs 111 and 115 to separate.When the relay 67 deenergizes, after the denergization of the line relay63, a circuit is closed through the release magnet 66 as follows: fromground G through springs shaft is away from its normal position) and tobattery. When the release magnet energizes, it restores the connector toits normal position, and when the shaft reaches normal, itforces theoff-normal springs 167 and 168 apart, leaving the-release magnet 66denergized. The release of the connector also removes the guardingground from the private bank contacts of the called line and opens theenergizing circuit of the cut-off winding 153 of the line switch C".

\Vhen the relay 98 of the selector F (lei ncrgizes, it cuts off theground from release relay 62 of the selector E and closes the circuit ofthe release magnet 200, which releases the selector F in the same manneras described for the connector H. The cutting off of the ground from therelease relay 62 of the selector E allows the relay 62 to deenergize,whereby the circuit of the release magnet 55 of selector E is energized,and the said selector is restored in the same way as the connector H.The denergization of the relay 62 also cuts off the holding ground fromthe cut-off return of the plunger arm withdrawsthe plunger from thebank, thereby disconnecting the calling line from selector E and re:

moving the guarding potential from the 7 master switch bank contact 86.The restoration of the cut-off armature 10 restores the line winding 32to the line of substation A.

From the foregoing it will be seen that I provide a metallicline-circuit-controlled automatic telephone exchange trunking system inwhich provision is made for preventing removal of the receivers at thesubstations from causing seizure of idle trunks at the exchange orcentral station. By a metallic circuit I mean a circuit that includesboth sides of the subscribers line in series for controlling thetrunking and other switches of the system, as distinguished from asystem in which operating grounds are employed at the substations, suchsystems being commonly known as three-wire systems. The

that here is a line switch for trunking purwithout seizing a trunk,because the seizure of a trunk is dependent upon the opening andimmediate closure of the line circuit at the substation. By taking downand then hanging up hi receiver the calling subscriber simply causes:his lineswitch to engage a trunk and" then release the same, inasmuchas the substation circuit must remain closed in order to keep the firstselector relay energized and the trunk thereby retained in connectionwith the calling line.

What I claim as my invention is 1. In a telephone system, a plurality oftrunks, selecting and connecting mechanism, a subscribers line, meansfor controlling said mechanism over the two sides of the line in series,to obtain connection with an idle trunk, means for preventing actuation'of said mechanism by the initial closure of the line, when thesubscriber calls, and means operated by the initial closure of the lineand the subsequent opening of the same for operating said mechanism,whereby connection with an idle trunk is effected.

2. In a telephone system, a line circuit, a

non-numerical switch allotted to said circuit, controllable over the twosides thereof in series, means for reventing actuation of said switch bythe initial closure of said circuit, and means operated by the initialclosure of the circuit and the subsequent opening of the same foroperating said switch, whereby a non-numerical switching operation iseffected.

3. In a telephone system, a line, a plurality of trunks, a switchindividual to said line, controllable over the two sides thereof inseries, for connecting the line with an idle trunk, means for preventingthe initial closure of the line from actuating said switch, a callingmechanism, and means responsive to the initial closure of the line, andto the subsequent opening of the same by the calling subscriber, foroperating said switch, whereby connection with an idle trunk is efi'ecte4. In a telephone system, a line, a switch therefor rovided with acontrolling magnet, trun s adapted to be seized by said switch, andmeans whereby said magnet is energized and said switch thereby operatedto seize a trunk in response to the openin of the line after the initialclosure thereo a In a telephone system, the combination of a line, aplunger attached thereto, a magnet for operating the plunger, a circuitfor energizing said magnet to actuate the plun- 1,24e,as4

ger, a normally open switch in said circuit, a circuit for energizingsaid magnet to operate the switch, said switch adapted to close saidcircuit in response to the opening of the line after the initial closurethereof, a plurality of trunks, and means whereby operation of theplunger connects the said line with an idle trunk.

6. In a telephone system, trunk lines, a main switch for seizing idlevtrunks, an auxiliary switch for controlling said main switch, andmechanical connection whereby operation of themain switch to seize atrunk seryes to restore the auxiliary switch to norma 7. In a telephonesystem, a main switch, an auxiliary switch, a magnet common to saidswitches, a line circuit for energizing the magnet to operate theauxiliary switch, a circuit for said magnet controlled by the auxiliaryswitch, and mechanical connection whereby actuation of the main switch acalled subscribers line, said numerical switches adapted to be operatedby a varying number of im ulses, depending upon the digit of the callesubscriber, means whereby the non-numerical switch selects an idle trunkextending to a numerical switch, and means for rendering the systeminoperative for trunking in response to the takin down of a receiver byany calling subscri er.

10. In a telephone system, a line, a switch therefor provided with acontrolling magnet having two windings, and means whereby the closingand opening of a circuit through one winding closes a circuit throughthe second winding thereof.

11. In a telephone system, line switches, a master switch therefor,trunk-release conductors extending from the line switches,

relay to put ground on the trunk-release conductors, as set forth.

12. In a telephone system, subscribers lines, line switches individualthereto, a master switch controlling said line switches, a

slow-acting relay for said master switch, a trunk-release conductor, andmeans for energizing said relay to thereby place ground on thetrunk-release conductor.

18. In a telephone system, line switches, a master switch therefor,trunk-release conductors extending from said line switches,

- an operating relay for said line switch, and

a relay controlling a circuit through the trunk-release conductors forsaid master switch, said relays connected in series, said controllingrelay being slow acting.

14. In a telephone system, a subscribers line, a non-numerical switchindividual to said line, means for. extended connection to said line,and means for preventing said non-numerical switch from operating toclose a circuit when the called subscriber answers, and if thesubscriber on said line retains his receiver 01f the hook until afterthe calling subscriber hangs up his receiver to release the connection.

15. In a telephone system, a subscribers line, a progressively movableswitch associated with said line for connecting said line withanother'line, means for extending connection from another calling lineto said first line, and automatic means for preventing saidprogressively movable'switch from. operating to close a circuit whenconnection ismade with the called line, and for preventing the operationof said progressively movable switch if the calling line is disconnectedfrom the called line while the apparatus of theycalled subscriber isstill across the line.

16. In a telephone system, a calling and a called line, a line switchfor each line including a line relay normally bridged across the lineand a trip magnet controlled thereby, means for cutting off the linerelay on the called line when connection is extendedlthereto, and meansfor preventing said trip magnet of the called line switch energlzingwhen the connection is disconnected before the called subscriber hangsup his receiver. 1 V

17. In a telephone system, a called line,

a line switch therefor, a circuit associated with said line switch,means for, establishing a connection with said'called line, and

means for preventing said line switch from operating to close saidcircuit either during said connection or after said connectionisreleased until the called subscriber hangs up his receiver. a

18. In a telephone system, a called-line,

a line switch therefor, a' circuit associated with said line switch,means for establishing a connection with said called line, and means forpreventing said line switchfrom operating to close said circuit eitherduring said connection or at the time said connection is released by thecalling subscriber.

19,. In a telephone system, a called line, a lineswitch therefor, acircuit associated with said line switch, means for establishing aconnection with said called line, and means for preventing said lineswitch from operating to close said circuit either during said'connection or as a result of the called teleconnection or as a result ofthe called line being closed at the time said'connection is released bythe callin subscriber.

Signed by me at hicago, Cook county,

Illinois, this 7th day of May, 1909.

EDWARD D, FALES.

Witnesses:

J. NonBY, .CLARENCE TAYLOR.

